Evaporator and centrifugal chiller provided with the same

ABSTRACT

Provided is an evaporator capable of, in a centrifugal chiller using a low pressure refrigerant used at a maximum pressure of less than 0.2 MPaG, preventing dry-out of a group of heat transfer pipes in an evaporator to increase heat transfer performance and to suppress reduced efficiency due to carryover of the low pressure refrigerant in a liquid phase to a turbo compressor side and a centrifugal chiller provided with same. An evaporator ( 7 ) comprises a pressure container ( 21 ) into which a refrigerant is compressed and introduced, a refrigerant inlet ( 22 ) provided on a lower portion of the pressure container, a refrigerant outlet ( 23 ) provided on an upper portion of the pressure container, a group of heat transfer pipes ( 25 ) that exchange heat with the refrigerant through the interior of the pressure container and a tabular refrigerant distribution plate ( 26 ) installed between the refrigerant inlet and the group of heat transfer pipes and in which refrigerant flow holes ( 26   a ) are drilled. The surface ratio of the refrigerant flow holes per unit area on the refrigerant distribution plate in an area (A 1 ) corresponding to a position near the upstream side of the group of heat transfer pipes is greater than that in another area (A 2 ).

TECHNICAL FIELD

The present invention relates to an evaporator gasifying a low pressurerefrigerant, and a centrifugal chiller provided with the same.

BACKGROUND ART

For example, as is well known, a centrifugal chiller used as a heatsource for district cooling and heating is configured to include a turbocompressor that compresses a refrigerant, a condenser that causes thecompressed refrigerant to be condensed, a control valve that causes thecondensed refrigerant to expand, an economizer that performs gas-liquidseparation of the expanded refrigerant, and an evaporator that causesthe expanded refrigerant to evaporate.

As disclosed in PTL 1, an evaporator includes a pressure containerhaving a cylindrical shell shape, in which a group of heat transferpipes serving as passages for a cooling target liquid such as water isarranged so as to penetrate the pressure container in a longitudinalaxial direction. In addition, inside the pressure container, adistribution plate (refrigerant distribution plate) having a number ofrefrigerant circulation holes bored therein is provided below the groupof heat transfer pipes, and an eliminator (demister) is provided abovethe group of heat transfer pipes.

A liquid-phase refrigerant compressed in the turbo compressor andcondensed in the condenser flows into the pressure container through arefrigerant inlet provided in a lower portion of the pressure containerand passes through a number of the refrigerant circulation holes in thedistribution plate, thereby performing heat exchange with the group ofheat transfer pipes while being diffused throughout the entire regioninside the pressure container. Consequently, the cooling target liquidflowing inside the group of heat transfer pipes is cooled, and thiscooled cooling target liquid is utilized as a cooling/heating medium forair conditioning or an industrial cooling liquid.

The liquid-phase refrigerant which has been subjected to heat exchangewith the group of heat transfer pipes boils and is gasified due to thetemperature difference. A liquid-phase part thereof is eliminated whenpassing through the eliminator, and only a gas-phase refrigerant issuctioned to the turbo compressor through a suction pipe connected to anupper portion of the pressure container and is compressed again.

In evaporators in the related art, inner diameters, boring intervals,and the like of the refrigerant circulation holes in the distributionplate are uniform. That is, the area ratio of the refrigerantcirculation holes per unit area in the distribution plate is uniformthroughout the entire region of the distribution plate.

In addition, the eliminator is disposed at a position sufficientlyhigher than the liquid level of the refrigerant inside the pressurecontainer. The reason is that so-called carry-over (gas-liquidentrainment) in which liquid droplets of the boiling refrigerant passthrough the eliminator and enter the suction pipe in a liquid phasestate is prevented and deterioration in efficiency of the turbocompressor is suppressed.

CITATION LIST Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No. 61-280359

SUMMARY OF INVENTION Technical Problem

Low pressure refrigerants such as R1233zd used at a maximum pressure ofless than 0.2 MPaG are expected as next generation refrigerants becausethey can improve efficiency of a centrifugal chiller and have a lowglobal warming potential.

Since such low pressure refrigerants are characterized by the gasspecific volume greater than that of a high pressure refrigerant such asR134a, when a low pressure refrigerant is subjected to heat exchangewith a group of heat transfer pipes and boils inside an evaporator,boiling froth increases. Therefore, so-called dry-out in which the groupof heat transfer pipes is locally surrounded by the boiling froth islikely to occur, so that heat transfer performance tends to deterioratecompared to a state where the group of heat transfer pipes is immersedin a refrigerant two-phase liquid.

In addition, in an upstream portion of the group of heat transfer pipesinside the evaporator, a refrigerant intensely boils due to thesignificant temperature difference between a cooling target liquidflowing inside the group of heat transfer pipes and the refrigerant.However, boiling of the refrigerant subsides in a downstream portion ofthe group of heat transfer pipes due to the reduced temperaturedifference. Therefore, it is difficult to set or adjust a liquid level(froth level) in a liquid-phase refrigerant pool inside the evaporator.

Moreover, since the gap flow velocity increases in the group of heattransfer pipes, there is concern over fatigue fracture caused due tofluid resistance applied to each of the heat transfer pipes. Inaddition, in a case where the low pressure refrigerant is used, sincethe volumetric flow rate of the gasified refrigerant suctioned from theevaporator to a turbo compressor is extremely greater than that of thehigh pressure refrigerant, the flow velocity of the gasified refrigerantinside the evaporator increases, and the liquid-phase refrigerant islikely to hitch the flow of the gasified refrigerant and to be carriedover to the turbo compressor side, so that there is concern overdeterioration in efficiency of the turbo compressor.

The present invention has been made in consideration of suchcircumstances, and an object thereof is to provide an evaporator in acentrifugal chiller using a low pressure refrigerant used at a maximumpressure of less than 0.2 MPaG, in which a group of heat transfer pipesis prevented from being dried out inside the evaporator, heat transferperformance is enhanced, and deterioration in efficiency caused due tothe liquid-phase low pressure refrigerant carried over to the turbocompressor side can be suppressed, and a centrifugal chiller providedwith the same.

Solution to Problem

In order to solve the problems, the present invention employs thefollowing means.

According to a first aspect of the present invention, there is providedan evaporator including a pressure container which extends in ahorizontal direction and into which a low pressure refrigerant used at amaximum pressure of less than 0.2 MPaG is introduced after beingcondensed; a refrigerant inlet which is provided in a lower portion ofthe pressure container; a refrigerant outlet which is provided in anupper portion of the pressure container; a group of heat transfer pipeswhich passes through an inside of the pressure container in alongitudinal axial direction and causes a cooling target liquid tocirculate inside the group of heat transfer pipes so as to heat exchangethe cooling target liquid with the low pressure refrigerant; and atabular refrigerant distribution plate which is installed between therefrigerant inlet and the group of heat transfer pipes inside thepressure container and in which refrigerant circulation holes are bored.An area ratio of the refrigerant circulation holes per unit area in therefrigerant distribution plate in a region corresponding to the vicinityof a position on an upstream side of the group of heat transfer pipes isgreater than the area ratio thereof in the remaining region.

As described above, the area ratio of the refrigerant circulation holesper unit area in the refrigerant distribution plate in the regioncorresponding to the vicinity of a position on an upstream side of thegroup of heat transfer pipes is greater than the area ratio thereof inthe remaining region. Therefore, a large portion of the low pressurerefrigerant introduced into the pressure container through therefrigerant inlet is distributed to the vicinity of a position on anupstream side of the group of heat transfer pipes. In addition, arelatively small amount of the low pressure refrigerant is distributedto the remaining position. Accordingly, the liquid level (froth level)in a low pressure refrigerant pool inside the pressure container iscaused to be even.

In the vicinity of a position on an upstream side of the group of heattransfer pipes inside the evaporator, since there is a significanttemperature difference between the low pressure refrigerant and thecooling target liquid flowing inside the group of heat transfer pipes,the low pressure refrigerant intensely boils. However, since arelatively large portion of the low pressure refrigerant is distributedto this position compared to the remaining position, the vicinity of aposition on an upstream side of the group of heat transfer pipes is incircumstances prevented from being surrounded by boiling froth of thelow pressure refrigerant and being dried out, so that it is possible tomaintain a state where the group of heat transfer pipes is immersed inrefrigerant two-phase liquid. Therefore, the cooling target liquidflowing inside the group of heat transfer pipes and the low pressurerefrigerant can be favorably subjected to heat exchange, so that it ispossible to enhance heat transfer performance of the group of heattransfer pipes.

In addition, the froth level in the low pressure refrigerant pool at anintermediate portion in the longitudinal axial direction of the pressurecontainer does not rise higher than those in both end portions in thelongitudinal axial direction. Therefore, when the refrigerant outletleading to a suction pipe of a turbo compressor is provided at theintermediate portion in the longitudinal axial direction of the pressurecontainer, the liquid-phase low pressure refrigerant is prevented fromhitching the flow of the gasified refrigerant and being carried over tothe turbo compressor side, so that it is possible to suppressdeterioration in efficiency of the turbo compressor.

In the evaporator, the refrigerant inlet may be configured to beprovided at an intermediate portion in the longitudinal axial directionof the pressure container. The area ratio of the refrigerant circulationholes in the refrigerant distribution plate in regions at end portionsof the refrigerant distribution plate in the longitudinal axialdirection may be configured to be greater than the area ratio thereof ina region at the intermediate portion in the longitudinal axialdirection.

According to the evaporator having the configuration described above, alarge portion of the low pressure refrigerant introduced into thepressure container through the refrigerant inlet provided at theintermediate portion in the longitudinal axial direction of the pressurecontainer is supplied to both the end portions in the longitudinal axialdirection inside the pressure container, and a relatively small portionthereof is supplied to the intermediate portion in the longitudinalaxial direction of the pressure container immediately above therefrigerant inlet. Therefore, the liquid level (froth level) in the lowpressure refrigerant pool inside the pressure container is caused to beeven, and the cooling target liquid flowing inside the group of heattransfer pipes and the low pressure refrigerant are favorably subjectedto heat exchange, so that it is possible to enhance heat transferperformance of the group of heat transfer pipes.

According to a second aspect of the present invention, there is providedan evaporator including a pressure container which extends in ahorizontal direction and into which a low pressure refrigerant used at amaximum pressure of less than 0.2 MPaG is introduced after beingcondensed; a refrigerant inlet which is provided in a lower portion ofthe pressure container; a refrigerant outlet which is provided in anupper portion of the pressure container; a group of heat transfer pipeswhich passes through an inside of the pressure container in alongitudinal axial direction and causes a cooling target liquid tocirculate inside the group of heat transfer pipes so as to heat exchangethe cooling target liquid with the low pressure refrigerant; and atabular refrigerant distribution plate which is installed between therefrigerant inlet and the group of heat transfer pipes inside thepressure container and in which refrigerant circulation holes are bored.A plurality of the refrigerant inlets are provided in a dispersed manneralong the longitudinal axial direction of the pressure container.

Since the low pressure refrigerant has significant specific volumecompared to a high pressure refrigerant, the volumetric flow ratethereof flowing into the evaporator through the refrigerant inlet issignificant and the dynamic pressure is high. However, when the pressureloss of the refrigerant distribution plate is increased as befits itscharacteristics, the velocity of the low pressure refrigerant spoutingout through the refrigerant circulation holes of the refrigerantdistribution plate increases, thereby leading to vibration or breakageof the group of heat transfer pipes.

According to the evaporator having the configuration described above,since a plurality of the refrigerant inlet are provided in a dispersedmanner along the longitudinal axial direction of the pressure container,the inflow velocity of the low pressure refrigerant can be reducedcompared to a case of having a single refrigerant inlet. Therefore, therefrigerant circulation holes of the refrigerant distribution plate canbe increased in diameter. Accordingly, the velocity of the low pressurerefrigerant spouting out through the refrigerant circulation holes isreduced, so that it is possible to prevent vibration or breakage of thegroup of heat transfer pipes.

In addition, the froth level in the low pressure refrigerant pool insidethe pressure container can be uniform by causing the low pressurerefrigerant to flow in equally through a plurality of refrigerant inletsthroughout the overall length of the pressure container in thelongitudinal axial direction. Accordingly, the group of heat transferpipes is prevented from being dried out and heat transfer performance isenhanced. Moreover, the liquid-phase low pressure refrigerant isrestrained from locally spouting upward or the like and being carriedover to the turbo compressor side, so that it is possible to avoiddeterioration in efficiency of the turbo compressor.

According to a third aspect of the present invention, there is providedan evaporator including a pressure container which extends in ahorizontal direction and into which a low pressure refrigerant used at amaximum pressure of less than 0.2 MPaG is introduced after beingcondensed; a refrigerant inlet which is provided in a lower portion ofthe pressure container; a refrigerant outlet which is provided in anupper portion of the pressure container; a group of heat transfer pipeswhich passes through an inside of the pressure container in alongitudinal axial direction and causes a cooling target liquid tocirculate inside the group of heat transfer pipes so as to heat exchangethe cooling target liquid with the low pressure refrigerant; and atabular refrigerant distribution plate which is installed between therefrigerant inlet and the group of heat transfer pipes inside thepressure container and in which refrigerant circulation holes are bored.A cross-sectional flow channel area from an outer opening portion of therefrigerant inlet to the pressure container is enlarged from the outeropening portion toward the pressure container.

According to the evaporator having the configuration described above,the cross-sectional flow channel area from the outer opening portion ofthe refrigerant inlet to the pressure container is enlarged toward thepressure container. Therefore, the flow velocity of the low pressurerefrigerant flowing through the refrigerant inlet is reduced toward thepressure container.

Therefore, vibration or breakage of the group of heat transfer pipes isprevented by reducing the velocity of the low pressure refrigerantspouting out through the refrigerant circulation holes of therefrigerant distribution plate. Moreover, the liquid-phase low pressurerefrigerant is restrained from locally spouting upward or the like andbeing carried over to the turbo compressor side, so that it is possibleto avoid deterioration in efficiency of the turbo compressor.

According to a fourth aspect of the present invention, there is providedan evaporator including a pressure container which extends in ahorizontal direction and into which a low pressure refrigerant used at amaximum pressure of less than 0.2 MPaG is introduced after beingcondensed; a refrigerant inlet which is provided in a lower portion ofthe pressure container; a refrigerant outlet which is provided in anupper portion of the pressure container; a group of heat transfer pipeswhich passes through an inside of the pressure container in alongitudinal axial direction and causes a cooling target liquid tocirculate inside the group of heat transfer pipes so as to heat exchangethe cooling target liquid with the low pressure refrigerant; and atabular refrigerant distribution plate which is installed between therefrigerant inlet and the group of heat transfer pipes inside thepressure container and in which refrigerant circulation holes are bored.The refrigerant inlet has a shape of a pipe connected to the pressurecontainer, and a flow velocity attenuation member attenuating a flowvelocity of the low pressure refrigerant is provided inside the pipe.

According to the evaporator having the configuration described above,the flow velocity attenuation member reduces the flow velocity of thelow pressure refrigerant flowing into the pressure container through therefrigerant inlet.

Therefore, vibration or breakage of the group of heat transfer pipes isprevented by reducing the velocity of the low pressure refrigerantspouting out through the refrigerant circulation holes of therefrigerant distribution plate. Moreover, the liquid-phase low pressurerefrigerant is restrained from locally spouting upward or the like andbeing carried over to the turbo compressor side, so that it is possibleto avoid deterioration in efficiency of the turbo compressor.

In the evaporator according to any one of those described above, thegroup of heat transfer pipes may be configured to include a group ofoutbound pipes extending from one end to the other end in thelongitudinal axial direction inside the pressure container, and a groupof inbound pipes communicating with the group of outbound pipes at theother end in the longitudinal axial direction inside the pressurecontainer and returning from the other end to the one end in thelongitudinal axial direction inside the pressure container. The group ofoutbound pipes may be configured to be disposed below and the group ofinbound pipes may be configured to be disposed above inside the pressurecontainer.

According to the evaporator having the configuration described above,the group of outbound pipes, in which the temperature difference betweenthe low pressure refrigerant and the cooling target liquid flowinginside the heat transfer pipes is significant and boiling of the lowpressure refrigerant becomes intense, is disposed in the lower portionof the pressure container, and the group of inbound pipes, in which thetemperature difference between the low pressure refrigerant and thecooling target liquid is small and boiling of the low pressurerefrigerant subsides, is disposed in the upper portion of the pressurecontainer.

Therefore, the low pressure refrigerant intensely boils below the liquidsurface in the low pressure refrigerant pool inside the pressurecontainer, and the liquid-phase refrigerant is unlikely to scatter onthe liquid surface in the low pressure refrigerant pool. Therefore, theliquid-phase refrigerant is prevented from being entrained by the flowof the gasified refrigerant and being carried over to the turbocompressor side, so that it is possible to suppress deterioration inefficiency of the turbo compressor.

In the evaporator according to any one of those described above, in thegroup of heat transfer pipes, a plurality of heat transfer pipe bundleseach having a plurality of heat transfer pipes bundled therein may beconfigured to be arrayed in a horizontal direction and gaps extending ina vertical direction may be configured to be formed across the heattransfer pipe bundles.

According to the evaporator having the configuration described above,the vertical gaps across the plurality of heat transfer pipe bundlesserve as passages for boiling froth of the low pressure refrigerantwhich has boiled through heat exchange with the group of heat transferpipes. Accordingly, the boiling froth can easily rise to the liquidsurface of the low pressure refrigerant. Therefore, the group of heattransfer pipes is prevented from being surrounded by boiling froth belowthe liquid surface of the refrigerant and being dried out, so that it ispossible to enhance heat transfer performance of the group of heattransfer pipes.

In the evaporator, the refrigerant circulation holes bored in therefrigerant distribution plate may be configured to be disposedvertically below the gaps.

According to the evaporator having the configuration described above,the flow of the low pressure refrigerant passing through the refrigerantcirculation holes bored in the refrigerant distribution plate and beingdischarged upward passes through the gaps and reaches the upper end ofthe group of heat transfer pipes, so that it is possible to enhance heattransfer performance of the group of heat transfer pipes.

In the evaporator according to any one of those described above, ademister positioned between the refrigerant outlet and the group of heattransfer pipes inside the pressure container and performing gas-liquidseparation of the refrigerant may be configured to be disposedimmediately above the group of heat transfer pipes.

In a case where the low pressure refrigerant is used, since the gas flowvelocity is high, the distance to a position where droplets of theliquid-phase refrigerant spouting upward are separated from thegas-phase refrigerant due to their dead weights becomes comparativelylong. Therefore, when the demister is installed at a position higherthan the position where the droplets are separated due to their deadweights, the distance from the liquid surface of the refrigerant to thedemister becomes long, and the pressure container increases in shelldiameter.

When the demister is disposed immediately above the group of heattransfer pipes as described above, the quantity of droplets spoutingupward is reduced by the demister, so that the carry-over amount can bereduced. Moreover, when the demister is disposed immediately above thegroup of heat transfer pipes, evaporated mist of the low pressurerefrigerant is promoted to be droplets having a large diameter in thespace above the demister, and the distance to the position where thedroplets are separated due to their dead weights is shortened, so thatit is possible to prevent the low pressure refrigerant from beingcarried over.

In the evaporator, the demister may be configured to be provided suchthat the entire circumference thereof is in contact with an innercircumference of the pressure container.

According to the evaporator having the configuration described above,the entire gas flow of the low pressure refrigerant inside the pressurecontainer has to pass through the demister, so that flow resistance ofthe gas flow increases. Therefore, the flow velocity distribution of thegas flow inside the pressure container is equalized, a local peak valueof the gas flow velocity decreases, and the rate of generating dropletsdrops. Moreover, the dead weight separation distance of droplets isshortened, so that it is possible to prevent the low pressurerefrigerant from being carried over.

In the evaporator according to any one of those described above, each ofthe heat transfer pipes configuring the group of heat transfer pipes maybe configured to be installed while penetrating a plurality of heattransfer pipe support plates having a plane direction intersecting thelongitudinal axial direction of the pressure container and beingdisposed at intervals in the longitudinal axial direction of thepressure container, and installation intervals of the heat transfer pipesupport plates in the vicinity of a position on an upstream side of thegroup of heat transfer pipes may be configured to be narrower than theinstallation intervals of the heat transfer pipe support plates in theremaining position.

In the vicinity of a position on an upstream side of the group of heattransfer pipes, since there is a significant temperature differencebetween the cooling target liquid flowing inside the group of heattransfer pipes and the low pressure refrigerant, the low pressurerefrigerant intensely boils, and the specific volume of boiling froththereof is greater than that of the high pressure refrigerant, therebygenerating significant vibration compared to a case of using a highpressure refrigerant. Therefore, there is concern that the group of heattransfer pipes will resonate with vibration of boiling froth and willbreak.

As described above, when the installation intervals of the heat transferpipe support plates in the vicinity of a position on an upstream side ofthe group of heat transfer pipes are caused to be narrower than theinstallation intervals of the heat transfer pipe support plates in theremaining position, resonance in the vicinity on an upstream side of thegroup of heat transfer pipes is suppressed and breakage can beprevented.

According to the present invention, there is provided a centrifugalchiller including a turbo compressor which compresses a low pressurerefrigerant used at a maximum pressure of less than 0.2 MPaG, acondenser which causes the compressed low pressure refrigerant to becondensed, and the evaporator according to any one of those describedabove which causes the expanded low pressure refrigerant to evaporate.

According to the centrifugal chiller having the configuration describedabove, in a case where the low pressure refrigerant is used, it ispossible to prevent the group of heat transfer pipes from being driedout due to boiling froth of the low pressure refrigerant inside theevaporator and to prevent droplets of the low pressure refrigerant frombeing carried over to the turbo compressor, so that it is possible toachieve improvement in efficiency of the low pressure refrigerant.

Advantageous Effects of Invention

As described above, according to the evaporator and the centrifugalchiller provided with the same of the present invention, in thecentrifugal chiller using a low pressure refrigerant used at a maximumpressure of less than 0.2 MPaG, the group of heat transfer pipes isprevented from being dried out inside the evaporator and heat transferperformance is enhanced. Moreover, it is possible to suppressdeterioration in efficiency caused due to the liquid-phase low pressurerefrigerant carried over to the turbo compressor side.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a general view of a centrifugal chiller according to anembodiment of the present invention.

FIG. 2 is a side view of an evaporator illustrating a first embodimentof the present invention seen in a direction of the arrow II in FIG. 1.

FIG. 3 is a longitudinal-sectional view of the evaporator taken alongline III-III in FIG. 2.

FIG. 4 is a longitudinal-sectional view of the evaporator taken alongline IV-IV in FIG. 2.

FIG. 5 is a side view of an evaporator illustrating a second embodimentof the present invention.

FIG. 6 is a longitudinal-sectional view of an evaporator illustrating athird embodiment of the present invention.

FIG. 7 is a view seen in a direction of the arrow VII in FIG. 6.

FIG. 8A is a longitudinal-sectional view of a refrigerant inletillustrating a fourth embodiment of the present invention.

FIG. 8B is a longitudinal-sectional view of another refrigerant inletillustrating the fourth embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

FIG. 1 is a general view of a centrifugal chiller according to anembodiment of the present invention. A centrifugal chiller 1 isconfigured in a unit state including a turbo compressor 2 thatcompresses a refrigerant, a condenser 3, a high-pressure expansion valve4, an economizer 5, a low-pressure expansion valve 6, an evaporator 7, alubricant tank 8, a circuit box 9, an inverter unit 10, an operationpanel 11, and the like. The lubricant tank 8 is a tank storing lubricantsupplied to bearings, a speed increaser, and the like of the turbocompressor 2.

The condenser 3 and the evaporator 7 are formed in cylindrical shellshapes having high pressure resistance and are disposed so as to beparallel and adjacent to each other in a state where their axial linesextend in a substantially horizontal direction. The condenser 3 isdisposed at a position relatively higher than the evaporator 7, and thecircuit box 9 is installed below thereof. The economizer 5 and thelubricant tank 8 are installed being interposed between the condenser 3and the evaporator 7. The inverter unit 10 is installed in an upperportion of the condenser 3, and the operation panel 11 is disposed abovethe evaporator 7. The lubricant tank 8, the circuit box 9, the inverterunit 10, and the operation panel 11 are disposed such that each thereofdoes not significantly stick out of the entire contour of thecentrifugal chiller 1 in a plan view.

The turbo compressor 2 is a known centrifugal turbine-type compressorwhich is rotatively driven by an electric motor 13. The turbo compressor2 is disposed above the evaporator 7 in a posture having its axial lineextending in the substantially horizontal direction. The electric motor13 is driven by the inverter unit 10. As described below, the turbocompressor 2 compresses a gas-phase refrigerant supplied through arefrigerant outlet 23 of the evaporator 7 via a suction pipe 14. A lowpressure refrigerant such as R1233zd used at a maximum pressure of lessthan 0.2 MPaG is used as the refrigerant.

A discharge port of the turbo compressor 2 and the upper portion of thecondenser 3 are connected to each other through a discharge pipe 15, andthe bottom portion of the condenser 3 and the bottom portion of theeconomizer 5 are connected to each other through a refrigerant pipe 16.In addition, the bottom portion of the economizer 5 and the evaporator 7are connected to each other through a refrigerant pipe 17, and an upperportion of the economizer 5 and a middle stage of the turbo compressor 2are connected to each other through a refrigerant pipe 18. Thehigh-pressure expansion valve 4 is provided in the refrigerant pipe 16,and the low-pressure expansion valve 6 is provided in the refrigerantpipe 17.

First Embodiment

FIGS. 2 to 4 illustrate a first embodiment of the evaporator 7.

As illustrated in FIG. 2, the evaporator 7 is configured to include apressure container 21 having a cylindrical shell shape extending in thehorizontal direction, a refrigerant inlet 22 provided in a lower portionof the pressure container 21, the refrigerant outlet 23 provided in anupper portion of the pressure container 21, a group of heat transferpipes 25 passing through the inside of the pressure container 21 in alongitudinal axial direction, a refrigerant distribution plate 26, and ademister 27.

Each of the refrigerant inlet 22 and the refrigerant outlet 23 isdisposed at an intermediate portion in the longitudinal axial directionof the pressure container 21. The refrigerant inlet 22 is formed in ashort pipe shape extending horizontally and tangentially from the bottomportion of the pressure container 21, and the refrigerant outlet 23 isformed in a short pipe shape extending vertically upward from the upperportion of the pressure container 21. As illustrated in FIG. 1, therefrigerant pipe 17 extending from the bottom portion of the economizer5 is connected to the refrigerant inlet 22, and the suction pipe 14 ofthe turbo compressor 2 is connected to the refrigerant outlet 23.

An inlet chamber 31 is provided on a lower side at one end (for example,the left end in FIG. 2) and an outlet chamber 32 is provided above theinlet chamber 31, as independent rooms inside the pressure container 21.In addition, a U-turn chamber 33 is provided as an independent room atthe other end (for example, the right end in FIG. 2) inside the pressurecontainer 21. All these chambers 31, 32, and 33 are disposed lower thanthe demister 27. An inlet nozzle 34 is provided in the inlet chamber 31,and an outlet nozzle 35 is provided in the outlet chamber 32.

As illustrated in FIGS. 2, 3 and 4, the group of heat transfer pipes 25includes a group of outbound pipes 25A extending from one end (the leftend in FIG. 2) to the other end (the right end in FIG. 2) in thelongitudinal axial direction inside the pressure container 21, and agroup of inbound pipes 25B communicating with the group of outboundpipes 25A at the other end in the longitudinal axial direction insidethe pressure container 21 and returning from the other end to the oneend in the longitudinal axial direction inside the pressure container21. Specifically, the group of outbound pipes 25A is arranged so as tolink the inlet chamber 31 and the lower portion of the U-turn chamber 33with each other, and the group of inbound pipes 25B is arranged so as tolink the outlet chamber 32 and the upper portion of the U-turn chamber33 with each other. That is, the group of outbound pipes 25A is disposedbelow inside the pressure container 21, and the group of inbound pipes25B is disposed above inside the pressure container 21.

For example, as a cooling target liquid to be cooled by the refrigerant,water (tap water, purified water, distilled water, or the like) flows inthrough the inlet nozzle 34. The water which has flowed in through theinlet chamber 31 flows through the group of outbound pipes 25A and makesa U-turn in the U-turn chamber 33. Thereafter, the water flows throughthe group of inbound pipes 25B and flows out through the outlet nozzle35 via the outlet chamber 32 as chilled water.

As illustrated in FIGS. 3 and 4, the group of outbound pipes 25A and thegroup of inbound pipes 25B configuring the group of heat transfer pipes25 have configurations in which a plurality (for example, four each) ofheat transfer pipe bundles 25 a each having a number of heat transferpipes bundled therein are arrayed in parallel in the horizontaldirection. Gaps S1 extending in a vertical direction are formed amongthe heat transfer pipe bundles 25 a. In addition, a gap S2 extending inthe horizontal direction is formed between the group of outbound pipes25A and the group of inbound pipes 25B.

As illustrated in FIG. 2, each of the heat transfer pipes configuringthe group of heat transfer pipes 25 (25A, 25B) is fixed inside thepressure container 21 while being supported by a plurality of heattransfer pipe support plates 37 inside the pressure container 21. Theheat transfer pipe support plates 37 are formed in flat plate shapeshaving a plane direction intersecting the longitudinal axial directionof the pressure container 21. The plurality of heat transfer pipesupport plates 37 are disposed at intervals in the longitudinal axialdirection of the pressure container 21 and are fixed to an inner surfaceof the pressure container 21. A number of penetration holes are bored inthe heat transfer pipe support plates 37, and the heat transfer pipesare tightly inserted through the penetration holes.

In the installation intervals of the heat transfer pipe support plates37 along the longitudinal axial direction of the pressure container 21,installation intervals L1 in the vicinity of a position on an upstreamside of the group of heat transfer pipes 25, that is, in the vicinity ofa position on an upstream side of the group of outbound pipes 25A (theleft side in FIG. 2) are set to be narrower than installation intervalsL2 in the remaining position. For example, L1 is approximately half ofL2.

Meanwhile, as illustrated in FIGS. 2 to 4, the refrigerant distributionplate 26 is installed between the refrigerant inlet 22 and the group ofheat transfer pipes (group of outbound pipes 25A) inside the pressurecontainer 21. The refrigerant distribution plate 26 is a tabular memberin which a number of refrigerant circulation holes 26 a are bored.

The area ratio of the refrigerant circulation holes 26 a per unit areain the refrigerant distribution plate 26 in a region A1 corresponding tothe vicinity of a position on an upstream side of the group of heattransfer pipes 25 (25A) is greater than the area ratio in the remainingregion, for example, in a region A2 corresponding to a position of anintermediate section of the group of heat transfer pipes 25. Inaddition, the area ratio of the refrigerant circulation holes 26 a inthe regions A1 and A3 at both end portions of the refrigerantdistribution plate 26 in the longitudinal axial direction is greaterthan the area ratio thereof in the region A2 at the intermediate portionin the longitudinal axial direction. As an example, the area ratios ofthe refrigerant circulation holes 26 a in the regions A1 and A3 canrange from 33% to 38%, and the area ratio of the refrigerant circulationholes 26 a in the region A2 can range from 24% to 33%. However, the arearatios are not limited to these regions only.

As illustrated in FIGS. 3 and 4, the refrigerant circulation holes 26 aof the refrigerant distribution plate 26 are disposed vertically belowthe gaps S1 which extend in the vertical direction and are formedbetween the plurality of heat transfer pipe bundles 25 a configuring thegroup of heat transfer pipes 25 (25A, 25B). That is, in a plan view, therefrigerant circulation holes 26 a are arrayed along a longitudinaldirection of the gaps S1.

As illustrated in FIGS. 2 to 4, the demister 27 is disposed between therefrigerant outlet 23 and the group of heat transfer pipes 25 (group ofinbound pipes 25B) inside the pressure container 21. For example, thedemister 27 is a member which has excellent air-permeability and inwhich wires are interwoven in a meshed state. The demister 27 performsgas-liquid separation of the low pressure refrigerant. The demister 27is not limited to the wire mesh, and other porous matters may beemployed as long as the matter is air-permeable.

The demister 27 is attached such that the entire circumference thereofis in contact with the inner circumference of the pressure container 21,the internal space of the pressure container 21 is divided into twoabove and below fiducially from the demister 27. In addition, theinstallation height of the demister 27 is set immediately above thegroup of heat transfer pipes 25. Specifically, the interval between thegroup of heat transfer pipes 25 and the demister 27 is set toapproximately twice the pipe disposition pitch. Meanwhile, acomparatively significant difference in height (for example,approximately 50% or more of the diameter of the pressure container 21)is provided between the demister 27 and the refrigerant outlet 23.

In the centrifugal chiller 1 including the evaporator 7 configured asdescribed above, the turbo compressor 2 is rotatively driven by theelectric motor 13, compresses a gas-phase low pressure refrigerantsupplied from the evaporator 7 via the suction pipe 14, and feeds thiscompressed low pressure refrigerant to the condenser 3 through thedischarge pipe 15.

Inside the condenser 3, when a high temperature low pressure refrigerantcompressed in the turbo compressor 2 is subjected to heat exchange withcooling water, condensed heat is cooled, so that the low pressurerefrigerant is condensed and liquefied. The low pressure refrigerantcaused to be in a liquid phase by the condenser 3 expands after passingthrough the high-pressure expansion valve 4 provided in the refrigerantpipe 16 extending from the condenser 3. The low pressure refrigerant istransported to the economizer 5 in a gas-liquid mixed state and istemporarily stored therein.

Inside the economizer 5, the low pressure refrigerant which has expandedthrough the high-pressure expansion valve 4 in a gas-liquid mixed stateis subjected to gas-liquid separation into a gas-phase part and aliquid-phase part. The liquid-phase part of the low pressure refrigerantseparated herein is caused to further expand through the low-pressureexpansion valve 6 provided in the refrigerant pipe 17 extending from thebottom portion of the economizer 5 and becomes a gas-liquid two-phaseflow, thereby being transported to the evaporator 7. In addition, thegas-phase part of the low pressure refrigerant separated in theeconomizer 5 is transported to a middle stage portion of the turbocompressor 2 via the refrigerant pipe 18 extending from the upperportion of the economizer 5 and is compressed again.

As illustrated in FIGS. 2 to 4, in the evaporator 7, the low pressurerefrigerant which has adiabatically expanded through the low-pressureexpansion valve 6 in a low temperature gas-liquid two-phase flow stateflows into the pressure container 21 through the refrigerant inlet 22,is dispersed in the longitudinal axial direction of the pressurecontainer 21 below the refrigerant distribution plate 26, and thenpasses through the refrigerant circulation holes 26 a of the refrigerantdistribution plate 26, thereby flowing upward. Then, a pool for the lowpressure refrigerant is formed inside the pressure container 21. Theliquid level in the low pressure refrigerant pool is automaticallyadjusted so as to be between the group of heat transfer pipes 25 and thedemister 27.

The group of heat transfer pipes 25 (25A, 25B) is in a state of beingimmersed in the low pressure refrigerant pool inside the pressurecontainer 21 and is subjected to heat exchange with the low pressurerefrigerant. Accordingly, water passing through the inside of the groupof heat transfer pipes 25 is cooled and turns into chilled water. Thischilled water is utilized as a cooling/heating medium for airconditioning, industrial cooling water, or the like.

The low pressure refrigerant which has evaporated (been gasified) due toheat exchange with the group of heat transfer pipes 25 is subjected togas-liquid separation by the demister 27. That is, when a gasified lowpressure refrigerant (gasified refrigerant) is headed for therefrigerant outlet 23 inside the pressure container 21, a fast flow isformed due to the characteristics of the low pressure refrigerant havingspecific volume greater than that of a high pressure refrigerant. Then,droplets of the liquid-phase refrigerant which have spouted upward fromthe low pressure refrigerant pool in a non-gasified state are entrainedby the fast flow of the gasified refrigerant and tend to come outthrough the refrigerant outlet 23, leading to a possibility ofoccurrence of carry-over.

However, since these droplets are captured by the porous demister 27,are separated, and fall into the low pressure refrigerant pool due togravity, the droplets are prevented from being carried over. Thegasified refrigerant which has been subjected to gas-liquid separationas described above comes out through the refrigerant outlet 23 and issuctioned and compressed again in the turbo compressor 2 via the suctionpipe 14. Thereafter, the freezing cycle is repetitively performed.

In the evaporator 7, the area ratio of the refrigerant circulation holes26 a in the refrigerant distribution plate 26 installed between therefrigerant inlet 22 and the group of heat transfer pipes 25 (25A, 25B)inside the pressure container 21 in the region A1 corresponding to thevicinity of a position on an upstream side of the group of heat transferpipes 25 (25A) is greater than the area ratio thereof in the remainingregion A2.

Therefore, a comparatively large portion of the low pressure refrigerantintroduced into the pressure container 21 through the refrigerant inlet22 is distributed to the vicinity of a position on an upstream side ofthe group of heat transfer pipes 25 (25A). In addition, a relativelysmall amount of the low pressure refrigerant is distributed to theremaining position. Accordingly, the liquid level (froth level) in thelow pressure refrigerant pool inside the pressure container 21 is causedto be even.

In the vicinity of a position on an upstream side of the group of heattransfer pipes 25 (25A) inside the pressure container 21, since there isa significant temperature difference between the low pressurerefrigerant and water flowing inside the group of heat transfer pipes 25(25A), the low pressure refrigerant intensely boils. However, asdescribed above, since a relatively large portion of the low pressurerefrigerant is distributed to this position compared to the remainingposition, the vicinity of a position on an upstream side of the group ofheat transfer pipes 25 (25A) is in circumstances prevented from beingsurrounded by boiling froth of the low pressure refrigerant and beingdried out, so that so that it is possible to maintain a state where thegroup of heat transfer pipes 25 (25A, 25B) is immersed in refrigeranttwo-phase liquid. Therefore, the cooling target liquid flowing insidethe group of heat transfer pipes 25 (25A, 25B) and the low pressurerefrigerant can be favorably subjected to heat exchange, so that it ispossible to enhance heat transfer performance of the group of heattransfer pipes 25 (25A, 25B).

As described above, the froth level in the low pressure refrigerant poolat the intermediate portion in the longitudinal axial direction of thepressure container does not rise higher than those in both the endportions in the longitudinal axial direction. Therefore, as in thepresent embodiment, when the refrigerant outlet 23 leading to thesuction pipe 14 of the turbo compressor is provided at the intermediateportion in the longitudinal axial direction of the pressure container21, the liquid-phase refrigerant is effectively prevented from hitchingthe flow of the gasified refrigerant and being carried over to the turbocompressor 2 side, so that it is possible to suppress deterioration inefficiency of the turbo compressor 2.

In addition, in the evaporator 7, the refrigerant inlet 22 is providedat the intermediate portion in the longitudinal axial direction of thepressure container 21, and the area ratio of the refrigerant circulationholes 26 a in the refrigerant distribution plate 26 in the regions A1and A3 at both the end portions of the refrigerant distribution plate 26in the longitudinal axial direction is greater than the area ratiothereof in the region A2 at the intermediate portion in the longitudinalaxial direction.

Therefore, a large portion of the low pressure refrigerant introducedinto the pressure container 21 through the refrigerant inlet 22 providedat the intermediate portion in the longitudinal axial direction of thepressure container 21 is supplied to both the end portions in thelongitudinal axial direction inside the pressure container 21, and arelatively small portion thereof is supplied to the intermediate portionin the longitudinal axial direction of the pressure container 21immediately above the refrigerant inlet 22. Therefore, the liquid level(froth level) in the low pressure refrigerant pool inside the pressurecontainer 21 is caused to be even, and water flowing inside the group ofheat transfer pipes 25 (25A, 25B) and the low pressure refrigerant arefavorably subjected to heat exchange, so that it is possible to enhanceheat transfer performance of the group of heat transfer pipes 25 (25A,25B).

Moreover, the group of heat transfer pipes 25 of the evaporator 7includes the group of outbound pipes 25A extending from one end to theother end in the longitudinal axial direction inside the pressurecontainer 21, and the group of inbound pipes 25B communicating with thegroup of outbound pipes 25A at the other end in the longitudinal axialdirection inside the pressure container 21 and returning from the otherend and to the one end in the longitudinal axial direction inside thepressure container 21. The group of outbound pipes 25A is disposed belowand the group of inbound pipes 25B is disposed above inside the pressurecontainer 21.

When the group of heat transfer pipes 25 is configured as describedabove, the group of outbound pipes 25A, in which the temperaturedifference between the low pressure refrigerant and water flowing insidethe heat transfer pipes is significant and boiling of the low pressurerefrigerant becomes intense, is disposed in the lower portion of thepressure container 21, and the group of inbound pipes 25B, in which thetemperature difference between the low pressure refrigerant and waterflowing inside the heat transfer pipes is small and boiling of the lowpressure refrigerant subsides, is disposed in the upper portion of thepressure container 21.

Therefore, the low pressure refrigerant intensely boils below the liquidsurface (deep part) in the low pressure refrigerant pool inside thepressure container 21, and the liquid-phase refrigerant is unlikely toscatter on the liquid surface in the low pressure refrigerant pool.Therefore, the liquid-phase refrigerant is prevented from beingentrained by the flow of the gasified refrigerant and being carried overto the turbo compressor 2 side, so that it is possible to suppressdeterioration in efficiency of the turbo compressor 2.

In the group of heat transfer pipes 25 (25A, 25B), a plurality of heattransfer pipes each having a plurality of heat transfer pipe bundles 25a bundled therein are arrayed in the horizontal direction and the gapsS1 extending in the vertical direction are formed across the heattransfer pipe bundles 25 a.

The vertical gaps S1 across the plurality of heat transfer pipe bundles25 a serve as passages for boiling froth of the low pressure refrigerantwhich has boiled through heat exchange with the group of heat transferpipes 25 (25A, 25B). Accordingly, boiling froth can easily rise to theliquid surface in the low pressure refrigerant pool. Therefore, thegroup of heat transfer pipes 25 (25A, 25B) is prevented from beingsurrounded by boiling froth below the liquid surface of the refrigerantand being dried out, so that it is possible to enhance heat transferperformance of the group of heat transfer pipes 25 (25A, 25B).

In addition, since the refrigerant circulation holes 26 a bored in therefrigerant distribution plate 26 are disposed vertically below the gapsS1, the flow of the low pressure refrigerant passing through therefrigerant circulation holes 26 a of the refrigerant distribution plate26 and being discharged upward passes through the gaps S1 and reachesthe upper end of the group of heat transfer pipes 25 (25A, 25B).Therefore, it is possible to enhance heat transfer performance of thegroup of heat transfer pipes 25 (25A, 25B).

In a case where the low pressure refrigerant is used as in thecentrifugal chiller 1, the gas flow velocity inside the pressurecontainer 21 of the evaporator 7 increases due to the characteristics ofthe low pressure refrigerant having specific volume greater than that ofa high pressure refrigerant. Therefore, the distance to a position wheredroplets of the liquid-phase refrigerant spouting upward from the lowpressure refrigerant pool inside the pressure container 21 are separatedfrom the gas-phase refrigerant due to their dead weights becomescomparatively long. Therefore, when the demister 27 is installed at aposition higher than the position where the droplets are separated dueto their dead weights, the distance from the liquid surface of therefrigerant to the demister 27 becomes long, and the pressure container21 increases in shell diameter.

In this evaporator 7, when the demister 27 is disposed immediately abovethe group of heat transfer pipes 25, the quantity of droplets spoutingupward from the low pressure refrigerant pool is reduced by the demister27, so that droplets of the low pressure refrigerant are restrained fromcoming out through the refrigerant outlet 23 (from being carried over).

Moreover, when the demister 27 is disposed immediately above the groupof heat transfer pipes 25, the space above the demister 27 relativelyincreases in height, evaporated mist of the low pressure refrigerant ispromoted to be droplets having a large diameter, and the distance to theposition where the droplets are separated due to their dead weights isshortened. Therefore, in this regard as well, it is possible to restrainthe low pressure refrigerant from being carried over.

Moreover, in this evaporator 7, the demister 27 is provided such thatthe entire circumference thereof is in contact with the entire innercircumference of the pressure container 21. Accordingly, the entire gasflow of the low pressure refrigerant inside the pressure container 21passes through the demister 27, so that flow resistance of the gas flowincreases. Therefore, the flow velocity distribution of the gas flowinside the pressure container 21 is equalized, a local peak value of thegas flow velocity decreases, and the rate of generating droplets drops.Moreover, the dead weight separation distance of droplets is shortened,so that it is possible to prevent the low pressure refrigerant frombeing carried over.

In addition, in this evaporator 7, the installation intervals L1 of theplurality of heat transfer pipe support plates 37 supporting each of theheat transfer pipes of the group of heat transfer pipes 25 in thevicinity of a position on an upstream side of the group of heat transferpipes 25 are set to be narrower than the installation intervals L2 inthe remaining position.

In the vicinity of a position on an upstream side of the group of heattransfer pipes 25, since there is a significant temperature differencebetween water flowing inside the group of heat transfer pipes 25 and thelow pressure refrigerant as described above, the low pressurerefrigerant intensely boils, and the specific volume of boiling froththereof is greater than that of the high pressure refrigerant, therebygenerating significant vibration compared to a case of using a highpressure refrigerant. Therefore, there is concern that the group of heattransfer pipes 25 will resonate with vibration of boiling froth and willbreak.

As described above, when the installation intervals L1 of the heattransfer pipe support plates 37 in the vicinity of a position on anupstream side of the group of heat transfer pipes 25 are caused to benarrower than the installation intervals L2 in the remaining position,installation rigidity in the vicinity on an upstream side of the groupof heat transfer pipes 25 is enhanced and resonance is suppressed, sothat it is possible to prevent breakage.

Second Embodiment

FIG. 5 is a side view of an evaporator illustrating a second embodimentof the present invention.

An evaporator 7A is different from the evaporator 7 (refrigerant inlet22) of the first embodiment in that a plurality of refrigerant inlets22A of the pressure container 21 are provided in a dispersed manneralong the longitudinal axial direction of the pressure container 21, andother configurations are the same. Therefore, the same reference signsare applied to parts having the same configurations, and description isomitted.

In the present embodiment, for example, two refrigerant inlets 22A aredispersed along the longitudinal axial direction of the pressurecontainer 21 so as to be separated from each other. The refrigerantinlet 22A may be provided at three or more locations. The refrigerantinlet 22A is the same as the refrigerant inlet 22 of the firstembodiment and is formed in a short pipe shape extending horizontallyand tangentially from the bottom portion of the pressure container 21.The caliber of each refrigerant inlet 22A is set to be smaller than thecaliber of the refrigerant inlet 22 of the first embodiment.

As described above, since the low pressure refrigerant has significantspecific volume compared to a high pressure refrigerant, the volumetricflow rate thereof flowing into the evaporator 7A is significant and thedynamic pressure is high. However, when the pressure loss is increasedby reducing the refrigerant circulation holes 26 a of the refrigerantdistribution plate 26, or the like as befits its characteristics, thevelocity of the low pressure refrigerant spouting out through therefrigerant circulation holes 26 a increases, thereby leading tovibration or breakage of the group of heat transfer pipes 25.

As in the evaporator 7A, when two, three, or more refrigerant inlets 22Aare provided so as to be separated from each other along thelongitudinal axial direction of the pressure container 21, the inflowvelocity of the low pressure refrigerant into the pressure container 21can be reduced compared to a case where a single refrigerant inlet 22 isprovided as in the first embodiment. Therefore, the refrigerantcirculation holes 26 a of the refrigerant distribution plate 26 canincrease in diameter. Accordingly, it is possible to reduce the velocityof the low pressure refrigerant spouting out through the refrigerantcirculation holes 26 a.

Accordingly, vibration or breakage of the group of heat transfer pipes25 is prevented, and the liquid-phase low pressure refrigerant isrestrained from locally spouting upward or the like and being carriedover to the turbo compressor 2 side, so that it is possible to avoiddeterioration in efficiency of the turbo compressor 2.

Third Embodiment

FIG. 6 is a longitudinal-sectional view of an evaporator illustrating athird embodiment of the present invention, and FIG. 7 is a view seen ina direction of the arrow VII in FIG. 6.

In an evaporator 7B, a cross-sectional flow channel area from an outeropening portion 22 a of the refrigerant inlet 22 provided in the bottomportion of the pressure container 21 to the pressure container 21 isenlarged from the outer opening portion 22 a toward the pressurecontainer 21. Specifically, an enlarged flow channel 22 b is providedbetween the outer opening portion 22 a and the pressure container 21.The rest of the configuration is similar to that of the evaporator 7 ofthe first embodiment in FIG. 3. Therefore, the same reference signs areapplied to parts having the same configurations, and description isomitted.

For example, the enlarged flow channel 22 b is formed in a box shape,and its cross-sectional flow channel area is set to be greater than thecross-sectional flow channel area of the refrigerant inlet 22. Forexample, the cross-sectional flow channel area of the enlarged flowchannel 22 b is set to be greater than the cross-sectional flow channelarea of the refrigerant inlet 22 by approximately two to five times. Theshape of the enlarged flow channel 22 b is not limited to only the boxshape, and other shapes may be employed as long as the cross-sectionalflow channel area is greater than the outer opening portion 22 a of therefrigerant inlet 22. For example, the enlarged flow channel 22 b mayhave a bulge shape or the like. In addition, it is possible to considerthat the refrigerant inlet 22 is formed to have a tapered pipe shapewhich increases in diameter from its outer opening portion 22 a towardthe pressure container 21 side, without providing the enlarged flowchannel 22 b.

In this manner, when the cross-sectional flow channel area from theouter opening portion 22 a of the refrigerant inlet 22 to the pressurecontainer 21 is enlarged toward the pressure container 21, the flowvelocity of the low pressure refrigerant flowing through the refrigerantinlet 22 is reduced toward the pressure container 21.

Therefore, vibration or breakage of the group of heat transfer pipes 25is prevented by reducing the velocity of the low pressure refrigerantspouting out through the refrigerant circulation holes 26 a of therefrigerant distribution plate 26. Moreover, the liquid-phase lowpressure refrigerant is restrained from locally spouting upward or thelike and being carried over to the turbo compressor 2 side, so that itis possible to avoid deterioration in efficiency of the turbo compressor2.

Fourth Embodiment

FIGS. 8A and 8B are longitudinal-sectional views of an evaporatorillustrating a fourth embodiment of the present invention.

An evaporator 7C is different from the evaporator 7 (refrigerant inlet22) of the first embodiment in that a flow velocity attenuation memberfor attenuating the flow velocity of the low pressure refrigerant isprovided inside the pipe of the refrigerant inlet 22, and otherconfigurations are the same.

As the flow velocity attenuation member, it is possible to consider thata porous plate (punching plate or the like) 22 c is installed inside thepipe of the refrigerant inlet 22 as illustrated in FIG. 8A or aplurality of baffle plates 22 d are installed inside the pipe of therefrigerant inlet 22 in a maze state as illustrated in FIG. 8B. As longas the flow velocity of the low pressure refrigerant inside the pipe ofthe refrigerant inlet 22 can be attenuated, a different member otherthan those described above may be installed as the flow velocityattenuation member.

In this manner, when the porous plate 22 c or the baffle plate 22 dserving as the flow velocity attenuation member is provided inside thepipe of the refrigerant inlet 22, the flow velocity of the low pressurerefrigerant flowing into the pressure container 21 through therefrigerant inlet 22 is reduced.

Therefore, vibration or breakage of the group of heat transfer pipes 25is prevented by reducing the velocity of the low pressure refrigerantspouting out through the refrigerant circulation holes 26 a of therefrigerant distribution plate 26. Moreover, the liquid-phase lowpressure refrigerant is restrained from locally spouting upward or thelike and being carried over to the turbo compressor 2 side, so that itis possible to avoid deterioration in efficiency of the turbo compressor2.

As described above, according to the evaporators 7, 7A, 7B, and 7C andthe centrifugal chiller 1 provided with these evaporator of the presentembodiment, in the centrifugal chiller 1 using a low pressurerefrigerant used at a maximum pressure of less than 0.2 MPaG, the groupof heat transfer pipes 25 is prevented from being dried out inside theevaporator and heat transfer performance is enhanced. Moreover, it ispossible to suppress deterioration in efficiency caused due to theliquid-phase low pressure refrigerant carried over to the turbocompressor 2 side.

The present invention is not limited to only the configurations of theembodiments described above, and changes or modifications can besuitably added. An embodiment having such changes or modifications addedthereto is also included in the scope of rights of the presentinvention. For example, the first to fourth embodiments may be combinedor the like.

REFERENCE SIGNS LIST

-   -   1 CENTRIFUGAL CHILLER    -   2 TURBO-COMPRESSOR    -   3 CONDENSER    -   7 EVAPORATOR    -   21 PRESSURE CONTAINER    -   22 REFRIGERANT INLET    -   22 a OUTER OPENING PORTION OF REFRIGERANT INLET    -   22 b ENLARGED FLOW CHANNEL    -   22 c POROUS PLATE (FLOW VELOCITY ATTENUATION MEMBER)    -   22 d BAFFLE PLATE (FLOW VELOCITY ATTENUATION MEMBER)    -   23 REFRIGERANT OUTLET    -   25 GROUP OF HEAT TRANSFER TUBES    -   25A GROUP OF OUTBOUND TUBES    -   25B GROUP OF INBOUND TUBES    -   25 a HEAT TRANSFER TUBE BUNDLE    -   26 REFRIGERANT DISTRIBUTION PLATE    -   26 a REFRIGERANT CIRCULATION HOLE    -   27 DEMISTER    -   37 HEAT TRANSFER TUBE SUPPORT PLATE    -   A1 REGION CORRESPONDING TO VICINITY OF POSITION ON UPSTREAM SIDE        OF GROUP OF HEAT TRANSFER TUBES (REGION AT END PORTION OF        REFRIGERANT DISTRIBUTION PLATE IN LONGITUDINAL AXIAL DIRECTION)    -   A2 REGION CORRESPONDING TO OTHER POSITIONS OF GROUP OF HEAT        TRANSFER TUBES (REGION AT INTERMEDIATE PORTION OF REFRIGERANT        DISTRIBUTION PLATE IN LONGITUDINAL AXIAL DIRECTION)    -   A3 REGION AT END PORTION OF REFRIGERANT DISTRIBUTION PLATE IN        LONGITUDINAL AXIAL DIRECTION    -   L1, L2 INSTALLATION INTERVAL OF HEAT TRANSFER TUBE SUPPORT PLATE    -   S1 GAP

1. An evaporator comprising: a pressure container which extends in ahorizontal direction and into which a low pressure refrigerant used at amaximum pressure of less than 0.2 MPaG is introduced after beingcondensed; a refrigerant inlet which is provided in a lower portion ofthe pressure container; a refrigerant outlet which is provided in anupper portion of the pressure container; a group of heat transfer pipeswhich passes through an inside of the pressure container in alongitudinal axial direction and causes a cooling target liquid tocirculate inside the group of heat transfer pipes so as to heat exchangethe cooling target liquid with the low pressure refrigerant; and atabular refrigerant distribution plate which is installed between therefrigerant inlet and the group of heat transfer pipes inside thepressure container and in which refrigerant circulation holes are bored,wherein an area ratio of the refrigerant circulation holes per unit areain the refrigerant distribution plate in a region corresponding to thevicinity of a position on an upstream side of the group of heat transferpipes is greater than the area ratio thereof in the remaining region. 2.The evaporator according to claim 1, wherein the refrigerant inlet isprovided at an intermediate portion in the longitudinal axial directionof the pressure container, and wherein the area ratio of the refrigerantcirculation holes in the refrigerant distribution plate in regions atend portions of the refrigerant distribution plate in the longitudinalaxial direction is greater than the area ratio thereof in a region atthe intermediate portion in the longitudinal axial direction.
 3. Anevaporator comprising: a pressure container which extends in ahorizontal direction and into which a low pressure refrigerant used at amaximum pressure of less than 0.2 MPaG is introduced after beingcondensed; a refrigerant inlet which is provided in a lower portion ofthe pressure container; a refrigerant outlet which is provided in anupper portion of the pressure container; a group of heat transfer pipeswhich passes through an inside of the pressure container in alongitudinal axial direction and causes a cooling target liquid tocirculate inside the group of heat transfer pipes so as to heat exchangethe cooling target liquid with the low pressure refrigerant; and atabular refrigerant distribution plate which is installed between therefrigerant inlet and the group of heat transfer pipes inside thepressure container and in which refrigerant circulation holes are bored,wherein a plurality of the refrigerant inlets are provided in adispersed manner along the longitudinal axial direction of the pressurecontainer.
 4. An evaporator comprising: a pressure container whichextends in a horizontal direction and into which a low pressurerefrigerant used at a maximum pressure of less than 0.2 MPaG isintroduced after being condensed; a refrigerant inlet which is providedin a lower portion of the pressure container; a refrigerant outlet whichis provided in an upper portion of the pressure container; a group ofheat transfer pipes which passes through an inside of the pressurecontainer in a longitudinal axial direction and causes a cooling targetliquid to circulate inside the group of heat transfer pipes so as toheat exchange the cooling target liquid with the low pressurerefrigerant; and a tabular refrigerant distribution plate which isinstalled between the refrigerant inlet and the group of heat transferpipes inside the pressure container and in which refrigerant circulationholes are bored, wherein a cross-sectional flow channel area from anouter opening portion of the refrigerant inlet to the pressure containeris enlarged from the outer opening portion toward the pressurecontainer.
 5. An evaporator comprising: a pressure container whichextends in a horizontal direction and into which a low pressurerefrigerant used at a maximum pressure of less than 0.2 MPaG isintroduced after being condensed; a refrigerant inlet which is providedin a lower portion of the pressure container; a refrigerant outlet whichis provided in an upper portion of the pressure container; a group ofheat transfer pipes which passes through an inside of the pressurecontainer in a longitudinal axial direction and causes a cooling targetliquid to circulate inside the group of heat transfer pipes so as toheat exchange the cooling target liquid with the low pressurerefrigerant; and a tabular refrigerant distribution plate which isinstalled between the refrigerant inlet and the group of heat transferpipes inside the pressure container and in which refrigerant circulationholes are bored, wherein the refrigerant inlet has a shape of a pipeconnected to the pressure container, and a flow velocity attenuationmember attenuating a flow velocity of the low pressure refrigerant isprovided inside the pipe.
 6. The evaporator according to claim 1,wherein the group of heat transfer pipes includes a group of outboundpipes extending from one end to the other end in the longitudinal axialdirection inside the pressure container, and a group of inbound pipescommunicating with the group of outbound pipes at the other end in thelongitudinal axial direction inside the pressure container and returningfrom the other end to the one end in the longitudinal axial directioninside the pressure container, and wherein the group of outbound pipesis disposed below and the group of inbound pipes is disposed aboveinside the pressure container.
 7. The evaporator according to claim 1,wherein in the group of heat transfer pipes, a plurality of heattransfer pipe bundles each having a plurality of heat transfer pipesbundled therein are arrayed in a horizontal direction and gaps extendingin a vertical direction are formed across the heat transfer pipebundles.
 8. The evaporator according to claim 7, wherein the refrigerantcirculation holes bored in the refrigerant distribution plate aredisposed vertically below the gaps.
 9. The evaporator according to claim1, wherein a demister positioned between the refrigerant outlet and thegroup of heat transfer pipes inside the pressure container andperforming gas-liquid separation of the low pressure refrigerant isdisposed immediately above the group of heat transfer pipes.
 10. Theevaporator according to claim 9, wherein the demister is provided suchthat the entire circumference thereof is in contact with an innercircumference of the pressure container.
 11. The evaporator according toclaim 1, wherein each of the heat transfer pipes configuring the groupof heat transfer pipes is installed while penetrating a plurality ofheat transfer pipe support plates having a plane direction intersectingthe longitudinal axial direction of the pressure container and beingdisposed at intervals in the longitudinal axial direction of thepressure container, and installation intervals of the heat transfer pipesupport plates in the vicinity of a position on an upstream side of thegroup of heat transfer pipes are narrower than the installationintervals of the heat transfer pipe support plates in the remainingposition.
 12. A centrifugal chiller comprising: a turbo compressor whichcompresses a low pressure refrigerant used at a maximum pressure of lessthan 0.2 MPaG; a condenser which causes the compressed low pressurerefrigerant to be condensed; and the evaporator according to claim 1which causes the expanded low pressure refrigerant to evaporate.
 13. Theevaporator according to claim 2, wherein the group of heat transferpipes includes a group of outbound pipes extending from one end to theother end in the longitudinal axial direction inside the pressurecontainer, and a group of inbound pipes communicating with the group ofoutbound pipes at the other end in the longitudinal axial directioninside the pressure container and returning from the other end to theone end in the longitudinal axial direction inside the pressurecontainer, and wherein the group of outbound pipes is disposed below andthe group of inbound pipes is disposed above inside the pressurecontainer.
 14. The evaporator according to claim 3, wherein the group ofheat transfer pipes includes a group of outbound pipes extending fromone end to the other end in the longitudinal axial direction inside thepressure container, and a group of inbound pipes communicating with thegroup of outbound pipes at the other end in the longitudinal axialdirection inside the pressure container and returning from the other endto the one end in the longitudinal axial direction inside the pressurecontainer, and wherein the group of outbound pipes is disposed below andthe group of inbound pipes is disposed above inside the pressurecontainer.
 15. The evaporator according to claim 4, wherein the group ofheat transfer pipes includes a group of outbound pipes extending fromone end to the other end in the longitudinal axial direction inside thepressure container, and a group of inbound pipes communicating with thegroup of outbound pipes at the other end in the longitudinal axialdirection inside the pressure container and returning from the other endto the one end in the longitudinal axial direction inside the pressurecontainer, and wherein the group of outbound pipes is disposed below andthe group of inbound pipes is disposed above inside the pressurecontainer.
 16. The evaporator according to claim 5, wherein the group ofheat transfer pipes includes a group of outbound pipes extending fromone end to the other end in the longitudinal axial direction inside thepressure container, and a group of inbound pipes communicating with thegroup of outbound pipes at the other end in the longitudinal axialdirection inside the pressure container and returning from the other endto the one end in the longitudinal axial direction inside the pressurecontainer, and wherein the group of outbound pipes is disposed below andthe group of inbound pipes is disposed above inside the pressurecontainer.
 17. The evaporator according to claim 2, wherein in the groupof heat transfer pipes, a plurality of heat transfer pipe bundles eachhaving a plurality of heat transfer pipes bundled therein are arrayed ina horizontal direction and gaps extending in a vertical direction areformed across the heat transfer pipe bundles.
 18. The evaporatoraccording to claim 3, wherein in the group of heat transfer pipes, aplurality of heat transfer pipe bundles each having a plurality of heattransfer pipes bundled therein are arrayed in a horizontal direction andgaps extending in a vertical direction are formed across the heattransfer pipe bundles.
 19. The evaporator according to claim 4, whereinin the group of heat transfer pipes, a plurality of heat transfer pipebundles each having a plurality of heat transfer pipes bundled thereinare arrayed in a horizontal direction and gaps extending in a verticaldirection are formed across the heat transfer pipe bundles.
 20. Theevaporator according to claim 5, wherein in the group of heat transferpipes, a plurality of heat transfer pipe bundles each having a pluralityof heat transfer pipes bundled therein are arrayed in a horizontaldirection and gaps extending in a vertical direction are formed acrossthe heat transfer pipe bundles.